Spatially resolved single-cell analysis uncovers protein kinase Cd-expressing microglia with anti-tumor activity in glioblastoma [Spatial Transcriptomics]

The glioblastoma (GBM) microenvironment contains resident immune cells with intrinsic anti-tumor potential, particularly microglia. Understanding the single-cell spatial heterogeneity and interactions between immune cells and brain tumor–initiating cells (BTICs) is essential for identifying therapeutic targets to reprogram immune responses and suppress BTIC growth. Using single-cell and spatial transcriptomics, we mapped immune cell populations in the GBM microenvironment and identified signaling networks mediating immune–cancer cell interactions. We discovered a previously unrecognized subset of microglia expressing protein kinase Cd (PKCd) with anti-tumor activity against BTICs. The presence of PKCd-expressing microglia was validated in human GBM specimens. Enhancing PKCd in microglia via adeno-associated virus or niacin increased phagocytosis of patient-derived BTICs in vitro and improved survival in GBM-bearing mice. Data from The Cancer Genome Atlas (TCGA) revealed that high PKCd expression correlates with increased apoptosis, phagocytosis, and immune signaling pathways. These findings offer highlight PKCd+ microglia as a promising therapeutic target in GBM. Overall design: Using GBM mouse modelts, mice were either treated with niacin or untreated, the tumors were resected from the mice and analyzed using spatial transcriptomics.